Unanswered Question

Hi all,

I am looking for a solution as follows;

2 Servers connected to an X.25 Switching Device that is connected to E1 lines. My problem is what Switching Equipment to Use, and then step by step process to configure the equipment. Further u can look at the following logical representation to understand more.

2 Servers ----- Switching or Routing Device ----- 8 E1 connections.

Thank you for anticipated help.


I have this problem too.
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The E1 Lines are not X.25, they are normal ISDN E1 connections. The Switching or Routing device will terminate the X.25 connections, i.e the Switching and Routing device will convert from X.25 to ISDN E1 in one direction, and then it will convert back from ISDN E1 to X.25 in the opposite direction. Logically we will have the following;

(X.25)----(Switching or Routing Device)----(ISDN E1)

Please note that the Servers located on the X.25 segment redundant Servers such that 1 will be active at some time, and then when it fails, the other server will take over automatically. so we need some automatic load-balancing mechanism on the Switchin or Routing Device that we will provide as the Solution.

Thank you for the time please. I appreciate.

Paolo Bevilacqua Sat, 06/02/2007 - 11:50

Ok. Now, the servers, are these connected with serial interfaces? And what L3 protocols do they use, IP, or what else ?

You mentioned ISDN E1, you mean PRI circuits to telco to make ISDN 64Kbps data calls, modem calls, or both ? That is to what device will they make/receive calls ? There must be a lot of them as 30 x 8 = 240.

The solution is to use a router, but what the best type is, depends on the above questions.

Thank you so much for finding time for me again.

There will be 8 E1 Connections which will be Leased Lines connecting Remote Sites. Ofcourse these E1 connections must carry data traffic, since data is what is generated by the X.25 Servers. They don't to use IP as the layer 3 protocol even. I wonder how this is possible however. The servers most likely will connect with Serial Interfaces. I don't mind if I can have your phone details to enable me provide further details to you so you can be clear with everything.

Thank you so much.

Paolo Bevilacqua Sat, 06/02/2007 - 14:30

Hi patmien,

So these are leased line E1s, not ISDN. Do you know what is on the other end of the E1 lines ?

Or any other detail? Because up to this point it's all a bit unclear. You can write me to the email in my profile, but I would prefer to continue the discussion here, where everyone can benefit from it.

Paolo Bevilacqua Sat, 06/02/2007 - 15:46


that way I understand this, is that remote users need to connect to the servers interactively with a terminal program.

You can do that with the users using a regular IP network, and doing telnet to the router.

Once they have reached the router via telnet, they will connect to the server via X.25. This is called an X.28 PAD.

If both server interfaces are active, router will use both. If only one is active, will use one only.

You have two choices to do this, the one-step and the two-steps method.

The one-step is also called "protocol translation" and the router will automatically convert telnet protocol to tX.28 PAD protocol. This requires an enterprise image.

The two-steps will log in the user into the router first, from there a "pad" command will connect them to the servers. You can automate this command and optionally ask for username/password before they connect to server.

Now for the hardware, the smaller router you can use is a 2801 equipped with 2 x HWIC-4T connected to the E1 lines with a V.35 DTE cables and external E1 DSU units (sometime incorrectly called modems), and 1 x WIC-2T with V.35 DCE cables to the servers.

If you want to eliminate the E1 DSU and connect the router directly to the E1 lines, you will need a bigger router, like a 7204 with any type of NPE. In this case you will need a board called PA-MC-8TE1 and the appropriate cables to the E1 circuits. You will also need a PA-4T board, again with V.35 DCE cables to connect the servers.

Hope this answers your question. Please remember to rate all useful posts using the scrollbox below!

Paolo Bevilacqua Sat, 06/02/2007 - 16:32


Can you check what is the interface type and speed used by the servers? If it is RS-232 "low speed" like 256Kbps or less, there are high-density 8-ports cards for the 2800/3800 series routers that you can use.

But if it is high speed, and/or you like to not use any external E1 DSU, you will need the 7200 router as mentioned before, and 2 x PA-8T cards. Once again you need to check the interface on the servers because these come in specialized types depending if it is V.35, RS-232, or X.21.

The price will vary dramatically between the 2800/3800 routers and the 7200.

As recognition to those providing answers, please rate all useful posts using the scrollbox below!


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